An international research team is warning that sea anemones are bleaching on a large scale.
The anemones are home to 28 species of fish, including the clownfish, which could also be at risk.
Researchers from the United States, Saudi Arabia, Australia and France surveyed 14,000 sea anemones from the Red Sea to the Pacific Ocean and found huge patches of the usually vibrant coral had bleached white.
While scientists have been studying coral bleaching for years, this is the first time a study has focused solely on whether or not anemones are bleaching too.
The study looked specifically at the species of sea anemones that shelter fish.
It found seven out of 10 are vulnerable to bleaching and in some places entire anemone beds had turned white.
Dr Ashley Frisch from the ARC Centre for Excellence for Coral Reef Studies at James Cook University says the researchers were alarmed by what they found.
"Normally anemones are relatively brightly coloured, they're rich in colour," he said.
"They can be brown, they can be pink or purple. They're just always rich in colour. A normal, healthy anemone is never white.
"What we find is when you go to places where there's been an increase in temperature in recent times the anemones are white like a piece of paper and that is not normal.
Dr Frisch says sea anemones living in Australian waters were not the worst affected and the Great Barrier Reef only had small patches of bleaching.
"In some places anemones form a significant proportion of the habitat or the cover of the sea floor," he said.
"In some places it's measured on a scale of tens of metres squared where you'll just be [seeing] enormous patches of white where the anemones have bleached.
"It's not like that on the Great Barrier Reef, fortunately. It's more isolated cases. But in some other places of the world where there's a significant and sustained increase in temperature, we've seen vast fields of anemones become bleached."
Dr Frisch says there is evidence some anemones can survive bleaching and recover but there is also a risk some will die off.
He says that poses a risk to 28 species of anemone fish that can not survive anywhere else.
"They might [survive] in an aquarium, but out there in the wild you never see anemone fish without an anemone," he said.
"The simple reality is without them they are exposed to predation and they just get eaten. We've done experiments to prove this. We've covered up an anemone and deprived the anemone fish of access to its house and very quickly that anemone fish gets eaten.
"We've also captured them and translocated them to a different place, dozens of metres away and within a very short time they just get eaten. So they are really dependent on that anemone for their survival."
The short-term study did not reveal exactly what is causing the bleaching.
Dr Frisch says that is the next step for him and his colleagues, along with finding out how the bleaching impacts anemone fish.
"Why is it that fish on bleached anemones appear skinny? Why do they decline in number? And what are the long term consequences for the fish?" he said.
"And of course, that has flow on effects for the aquarium trade and for the wellbeing of lots of fisherman who catch anemone fish for their livelihoods."